Hi Bruce,
The behaviour you described is correct from a DS point of view. Dynamic
references can be bound at any time, from any thread before, during or after
activation. They can even be bound/unbound multiple times during activation.
Therefore you cannot rely on a dynamic reference from your activate method or
vice versa.
Even if you make this a static reference, those are required to invoke before
activate, therefore your code will be guaranteed to throw NPE (whereas your
current code only *probably* NPEs).
There are a couple of options. Does your ‘processor’ object actually depend on
anything that is initialised in component activation? I.e., does it need access
to ComponentContent or BundleContext, or the component config? If not then you
can just make it a final field and initialise it during construction.
If it does then you have to defer the invocation of processor.process(). I
suggest you use a final List of Foo objects (or ServiceReference<Foo>). The
bindFoo method detects whether the processor exists yet, and if not it just
adds the Foo onto the list. That list should be drained by the activate method
after it initialises the processor. Note you will have to write this with
thread safety because, as I said, the activate and bind/unbindFoo methods can
be called from separate threads.
Obviously this is a little complex so it’s far better if you can just
initialise processor in your constructor.
Neil
> On 12 May 2017, at 08:05, Bruce Jackson <bruce.jack...@myriadgroup.com> wrote:
>
> Hi Everyone
>
> I was wondering if anyone could provide some advice:
>
> I have a component of the form:
>
> @Component(name="Bar")
> public class MyComponent {
>
> private MyServiceProcessor processor;
>
> @Activate
> public void activate(ComponentContext cc) {
>
> processor = new MyServiceProcessor();
>
> }
>
> @Deactivate
> public void deactivate(ComponentContext cc) {
>
> }
>
> @Reference(cardinality = ReferenceCardinality.MULTIPLE)
> public void bindFoo(ServiceReference<Foo> ref) {
>
> /* some code here */
> processor.process(ref.getService());
> /* some more code here */
>
> }
>
> public void unbindFoo(ServiceReference<Foo> ref) {
>
> }
>
> }
>
> The problem here is that the bindFoo() method is called by the SCR before the
> activate and thus a null pointer exception is thrown in the
> processor.process() call.
> This is perhaps not surprising, but it is not ideal for a component that is
> ‘lazy’ about the other services that it wants to discover. I could clearly
> move this functionality into a ServiceTracker which I create in the
> activate() but was wondering if there was another approach that allowed me to
> do this via DS and annotations?
>
> Best regards
>
> Bruce
>
>
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